Clindamycin for Mixed S. aureus and Group A Streptococcus Infection
Clindamycin (Cleocin) is an excellent choice for treating infections with both Staphylococcus aureus and Group A Streptococcus pyogenes, as it provides coverage against both organisms and has the added benefit of inhibiting toxin production, which is particularly valuable for streptococcal infections. 1
Why Clindamycin Works for This Mixed Infection
Clindamycin is specifically recommended by the Infectious Diseases Society of America (IDSA) as a single-agent option when coverage for both β-hemolytic streptococci (including Group A Strep) and Staphylococcus aureus is desired. 1 This makes it uniquely suited for your culture results showing both organisms.
Dosing Recommendations
For adults with skin and soft tissue infections:
- Oral: 300-450 mg four times daily for 7 days 1
- Intravenous: 600 mg every 8 hours 1
- For severe infections: 600-900 mg every 6 hours IV 1
Critical Considerations Before Using Clindamycin
Check for Methicillin Resistance
The major caveat is that clindamycin has limited activity against methicillin-resistant S. aureus (MRSA), with only approximately 60-70% of MRSA strains remaining susceptible. 2 If your culture identifies the S. aureus as MRSA, you must verify clindamycin susceptibility testing before proceeding. 1
Inducible Resistance Risk
Clindamycin has potential for cross-resistance and emergence of resistance in erythromycin-resistant strains through inducible resistance mechanisms. 1 The IDSA guidelines note this is particularly important for MRSA isolates. 1 Request a D-test if the isolate is erythromycin-resistant but appears clindamycin-susceptible to detect inducible clindamycin resistance. 1
Resistance Development in Endocarditis
Avoid clindamycin monotherapy for S. aureus endocarditis, as clinical relapses and development of resistance to clindamycin, lincomycin, and erythromycin have been documented during treatment. 3 This is not relevant for most skin/soft tissue infections but critical if bacteremia or endocarditis is present. 4
Advantages of Clindamycin for This Infection
Toxin Inhibition
Clindamycin inhibits toxin production by both S. aureus and S. pyogenes, which is particularly valuable for necrotizing infections or toxic shock-like syndromes. 5 This antitoxin effect provides benefit beyond simple bacterial killing. 5, 6
For Group A Streptococcus specifically, clindamycin added during mid-log phase growth effectively inhibits production of NAD+ glycohydrolase, streptolysin O, and streptococcal inhibitor of complement. 6
Tissue Penetration
Clindamycin penetrates and accumulates within leukocytes, making it particularly valuable for treating S. aureus infections resulting in large abscesses. 4
When to Choose Alternative Agents
If the S. aureus is methicillin-susceptible (MSSA) and you want a first-line agent:
- Cefazolin 1 g every 8 hours IV is preferred for severe infections 1
- Cephalexin 500 mg every 6 hours orally for outpatient treatment 7
If MRSA is confirmed or suspected with high local resistance rates:
- Vancomycin is the parenteral drug of choice 1
- Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily can be combined with a β-lactam (like amoxicillin) to cover both organisms 1
- Linezolid 600 mg twice daily covers both organisms as monotherapy 1
Treatment Duration
The recommended duration is 5-7 days for most skin and soft tissue infections, but extend treatment if the infection has not improved within this timeframe. 1 For complicated infections requiring IV therapy, 7-14 days is standard. 1
Common Pitfall to Avoid
Do not use clindamycin if local MRSA resistance rates exceed 10%, unless susceptibility testing confirms the isolate is susceptible. 1 The IDSA specifically recommends clindamycin as an empirical option for hospitalized children only when clindamycin resistance rates are low. 1